The present invention relates to the field of electric machines for use in a motor vehicle.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
An electric machine for use in a motor vehicle should be able to provide a highest possible torque or power density. This, however, is accompanied by a high current density within the stator coils that is a major cause for overall losses of the electric machine. As a result, aspects of thermal stress resistance of such electric machines become increasingly the focus in terms of industrial development. Since also the properties of materials used for the manufacture of such an electric machine are greatly temperature-dependent, various approaches have been proposed to meet the need for cooling so as to satisfy the desired electromagnetic function as well as thermal and mechanical demands.
One approach in the art involves the use of cooling fluid to flow through the stator and stator coils. Cooling fluid flows hereby through the slots of the laminated core and can flow either through intermediate spaces between several stator coils in a slot or through particular recesses in individual stator coils. A seal is provided to seal the stator against the rotor in circumferential and axial directions. The presence of such a seal adversely affects, however, the electromagnetic behavior of the electric machine through increase of the air gap thereof.
US 2012/0248904 A1 discloses a liquid-cooled stator and rotor assembly for use as an electric motor or generator. The stator includes a housing having a first end bell, a second end bell, and at least one fluid orifice in the first end bell. A stator is fixed within a stator cavity of the housing. The stator includes a stator core and a plurality of windings for conducting a flow of electricity. A rotor for magnetically interacting with the stator is also included, the rotor being rotatably mounted between the first end bell and the second end bell within a rotor cavity. A first sealing ring and a second sealing ring are provided to form a fluid seal against the respective end bells and against a portion of the stator such that a cooling fluid entering the stator cavity via the orifice does not enter the rotor cavity. In this type of electric machines, the stator core contacts the cooling fluid so that the electric machine can be used only for a particular cooling fluid that is not corrosive to the stator core so that the application of efficient cooling fluids for cooling purposes is not possible.
It would therefore be desirable and advantageous to address these afore-mentioned problems and to obviate other prior art shortcomings.